The present invention relates to the field of radiology and, more specifically, to apparatus for converting a commercially available film assembly, primarily intended for conventional photographic applications, into a radiographic film assembly by incorporating an intensifying screen or other types of radiographic elements thereinto that emit light in the visible spectrum to expose the film when struck by X-ray or nuclear energy.
In the illustrated embodiment, the conventional film assembly is a 4".times.5"self-developing film packet of the type manufactured and marketed by Polaroid Corporation, Cambridge, Massachusetts, under the trade designations Types 51, 52, 55 P/N, 57 and 58, among others, and essentially configured as disclosed in commonly-assigned U.S. Pat. No. 3,586,501.
Each of these film assemblies includes a photosensitive or negative component and a retractable opaque cover envelope having a positive or image receiving sheet releasably secured to one interior surface thereof and a rupturable pod of fluid processing composition secured to an opposite interior surface thereof.
The photosensitive component includes a negative sheet having a photosensitive emulsion or negative layer thereon and a metal retaining clip secured to the trailing end of the negative sheet.
The opaque cover envelope is sealed along three of its sides and the negative sheet is inserted thereinto through an opening at the trailing end. When the negative sheet is at its fully inserted position, the positive or image receiving sheet is disposed in face-to-face relation with the negative sheet and the open end of the envelope is slidably received in the metal clip to light seal the trailing end of the assembly.
The film assembly is configured for use with a film holder-processor, hereinafter termed a "film holder" such as the Polaroid Land 4.times.5 Film Holder No. 545 sold by Polaroid Corporation and described in commonly-assigned U.S. Pat. No. 3,505,939.
The film holder has an exposure opening in a front wall thereof and is adapted to be mounted on the back of a 4.times.5 view camera or the like. The film assembly is advanced through a slot in the end of the holder to a fully inserted position where a latching mechanism releasably engages the metal clip thereby securing the trailing end of the negative sheet. With the negative sheet secured, the envelope is partially withdrawn from the holder to a retracted position thereby uncovering the photosensitive portion of the negative sheet for exposure to image forming light transmitted through the exposure aperture. Following exposure, the envelope is returned to its closed or fully inserted position thereby recovering the negative sheet and positioning the positive sheet in face-to-face relation with the exposed photosensitive portion. Upon release of the latch holding the metal clip, a pair of pressure applying rollers adjacent the withdrawal slot move into position to define a narrow gap therebetween. The film assembly is then withdrawn from the holder between the pressure applying rollers which rupture the pod and distribute the fluid processing composition between the positive and negative sheets to initiate a well-known development and diffusion transfer process. Following a suitable imbibition period, the envelope is opened and the superposed sheets are peeled apart to reveal a positive image on the image receiving sheet.
The idea of inserting an intensifying screen or other type of radiographic element into the opaque envelope of such a film assembly to convert it for radiographic use is well-known in the prior art.
For example, commonly-assigned U.S. Pat. No. 3,462,599 is directed to a radiographic apparatus for inserting a radiographic element comprising an intensifying screen or a radioactive source in combination with an intensifying screen or layer into a self-processing film pack of the type described above.
The radiographic element is mounted on a thin magnetically attractable metal carrier sheet that is inserted into the 4".times.5" film holder-processor to position it on top of a film assembly therein. The film holder is then inserted into a support frame that has a movable permanent magnet carrier manipulator thereon. To insert the carrier into the opaque cover envelope, the permanent magnet is located in a neutral position where it does not magnetically influence the metal carrier. The envelope is retracted so that gravitational force urges the leading end of the carrier into engagement with the now uncovered negative sheet. As the envelope is pushed back into the holder, it slides over both the negative sheet and the superposed carrier thereby effecting insertion of the radiographic element into the envelope in face-to-face relation with the photosensitive portion of the negative.
Movement of the permanent magnet to a second neutral position releases the latch holding the metal clip on the end of the film assembly so it may be withdrawn from the film holder for exposure. Following exposure, the film assembly is reinserted into the film holder where its trailing end clip is engaged by the latch mechanism. Once again, the envelope is withdrawn to its retracted position. Now, the permanent magnet is moved to a third position where it magnetically attracts the carrier and lifts its leading end away from the negative sheet. With the carrier held in its raised position spaced from the negative sheet, the envelope is pushed back into the holder so as to pass between the carrier and the negative sheet. Thus, the negative sheet is enclosed by the opaque envelope and the carrier mounting the radiographic element remains on the exterior of the envelope. Thereafter, the clip holding latch is released and the rollers are moved to their pressure applying position so that the processing fluid is distributed between the positive and negative sheets in response to withdrawing the film assembly from the film holder-processor.
While the above-described apparatus performs satisfactorily, it does have certain disadvantages. For example, the need for a permanent magnet, the magnetically attractable metal carrier and a metal plate for neutralizing the force of the magnet when it is in two of its three operative positions increases materials costs. Movably mounting the magnet and providing adequate structure to insure that it is positively located in each of its three operative positions increases the mechanical complexity of the device thereby adding to manufacturing costs.
Therefore, it is object of the present invention to provide apparatus for associating and disassociating a radiographic element with a conventional film unit, of the type described above, which is easy to use, simply constructed and low in cost.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.